1. Field of the Invention
The cooling of sulfur-bearing slag such as blast furnace slag is conventionally accomplished by the use of water, for example by pouring it onto the slag in pits, by pouring molten slag into a reservoir of water, or dampening the ground on which thin layers of molten slag are poured. The slag is cooled by the water in order to permit its handling within a reasonable time after pouring. However, this cooling has heretofore been accompanied by the release of hydrogen sulfide which is malodorous, noxious and therefore considered an undesirable air pollutant. In fact, recently enacted anti-pollution codes in some localities prohibit the water quenching of slag except under conditions which prevent the discharge of all hydrogen sulfide or other air contaminants into the open air.
2. Description of the Prior Art
No process is presently known which inhibits the formation of objectionable hydrogen sulfide during the water cooling of hot sulfur-bearing slag. The Battelle Memorial Institute, Columbus, Ohio, in a 1968 paper by F. H. Woehlbier and G. W. P. Rengstorff entitled "Preliminary Study of Gas Formation During Blast-Furnace Slag Granulation with Water," discusses the possible reasons for the creation of hydrogen sulfide and suggests two approaches for suppressing its formation. One is to add oxidants to the slag prior to granulation, that is, while the slag is in its molten state. This suggestion is believed unfeasible because of the inability to stir an oxidant into molten slag while in a large ladle. The second suggestion is to conduct the granulation in such a manner as to destroy any possible protective gaseous layers which prevent combustion of the hydrogen sulfide, for example by a strongly agitated water bath or in a waterair jet. However, this process would create very fine, friable weak particles of insufficient strength or size to be used for example as an aggregate road base.
Knuppel U.S. Pat. No. 2,829,959 is a process for producing slag wool in which the slag is desulfurized by subjecting molten slag to an oxidizing treatment. Aside from being an entirely different process than that of the present invention, the Knuppel method would result in sulfur dioxide, an undesirable contaminant, being released into the atmosphere. Other U.S. patents such as Elbers U.S. Pat. No. 278,002, Wuth U.S. Pat. No. 643,856, Parsons U.S. Pat. No. 1,551,616, and Smyers U.S. Pat. No. 3,249,402 shows various methods for the removal or recovery of sulfur from blast furnace slag, but none of these are related to the present invention.